Conveying system for work pieces

ABSTRACT

A circuit-like system which includes a lower conveyor line, an upper conveyor line and a pair of lift or transfer mechanisms at the end of each line constructed for moving a work piece. A travel and hoist mechanism and a beam assembly are provided for discontinuously moving work pieces along the lower line and raising and lowering them for treatment. A hook assembly is provided for restraining the downward movement of a work piece at a selected location when the hook assembly is in an operative position.  
     The lift or transfer mechanism is provided which includes telescoping arms for grasping a work piece, which arms are carried by a vertically moveable carrier that is mounted in a stationary frame.

BACKGROUND OF THE INVENTION

[0001] This invention relates to a circuit-like conveying system wherebywork pieces are moved to various treatment stations and moreparticularly to a system for moving the work pieces along a generallyhorizontal path in a discontinuous manner and vertically as required andto a related transfer or lift mechanism.

[0002] Conveyors for moving work pieces from place to place or totreatment stations are well known, One conveyor type moves work piecesfrom place to place in a continuous manner. Another type of conveyormoves the work pieces in a start/stop or discontinuous manner so thatthe work pieces can be treated (usually dipped) at various stations.Such treatment may include painting, plating, cleansing and the like.Conveyors of this type move the work piece along a horizontal path, thenthe work piece may be stopped, moved vertically downwardly at a givenstation so as to dip the work piece in a treatment tank, upwardly out ofthe tank and then back along the horizontal path. A transfer or liftmechanism, positioned at the end of the conveyor, is provided for movingthe work piece from one path or conveyor line to another. Conveyors ofthis type may receive untreated pieces from a remote conveyor anddeliver treated pieces to the remote conveyor.

[0003] In a circuit-like conveying system there is provided a first orlower horizontal conveyor line or path along which the pieces are moved,stopped, lowered, treated, raised and moved to the end of the line. Atthe end of the line the pieces exit the first horizontal conveyor, areretrieved and moved vertically upwardly or delivered to the entrance toa second or upper horizontal line which may be a drying oven or dryingstation. The pieces are moved horizontally along a second or drying line(usually in an opposite direction to the first conveyor) to the exit ofthe second line and may be returned to the remote conveyor and anuntreated piece can be retrieved and delivered to the entrance for thefirst conveyor. This type of movement is seen in connection with platingmachines and the like and generally defines a circuit. Machines of thistype are known in the prior art but are believed to be complex andunreliable.

[0004] It is an object of this invention to provide an improvedcircuit-like conveying system of the type described above which is lesscomplex and more reliable than machines of the prior art.

[0005] Systems of the type described herein include a transfer or liftstation at the exit end of the first line for retrieving treated piecesand moving the pieces upwardly for delivery to the entrance to a secondconveyor line for drying or the like. A transfer station at the exit endof the second line is provided for removing dried pieces and deliveringthem to a remote conveyor. The transfer station or lift can alsoretrieve untreated pieces from the remote conveyor and move or deliverthem into the entrance end of the first treatment line. Transfer or liftmechanisms in the prior art tend to be complex, unreliable and notidentical at the respective ends of the lines.

[0006] It is an object of this invention to provide improved transferstations or lift mechanisms which are less complex, reliable andsubstantially identical so that one can be placed at the end of thetreatment line or the drying line for the movement of work pieces.

[0007] With respect to the first conveyor, the work pieces aresubstantially equally spaced from one another and are moved downwardlyas a group into treatment tanks, treated, moved upwardly as a group andthen moved on to the next station for additional treatment.

[0008] It is an object of this invention to provide an improved systemfor moving the work pieces as a group a fixed distance, dipping theminto a plurality of tanks for treatment, raising them and moving them onto the next station.

[0009] These and other objects of this invention will become apparentfrom the following description and appended claims.

SUMMARY OF THE INVENTION

[0010] There is provided by this invention an improved circuit-likeconveying apparatus for the movement of work pieces between varioustreatment stations and a transfer station or a lift mechanism forretrieving work pieces from one conveyor and delivery to a secondconveyor. The apparatus includes a frame and a plurality of treatmentstations positioned relative to the frame. A travel mechanism carried onthe frame is moveable relative to the frame between adjacent treatmentstations. A hoist mechanism, which is carried on the travel mechanism,cooperates in moving the work pieces between lower treatment and uppermovement positions. A beam, which cooperates with the hoist mechanism,extends along the frame and is connected to the hoist mechanism,preferably by an electrically driven retractable and extendablemechanism, carries or supports the work pieces and is constructed torelease work pieces when they are in treatment tanks. By thisconstruction a work piece can be releasably secured to the beam, loweredfor treatment, raised and moved horizontally from the entrance to theexit of the lower or treatment line. The work pieces are releasablysecured to the beam and are constructed to be released when positionedin a treatment station tank so that the beam can be moved rearwardly onestation and then raised so as to grasp a subsequent or trailing workpiece and move it forwardly to the next station. In this way the workpieces are moved from tank to tank.

[0011] A transfer station or lift apparatus for retrieving a work pieceis provided at the exit end of the conveyor or treatment line and isarranged to retrieve a work piece at the exit end and transport the workpiece to the entrance end of another conveyor which is horizontallydisposed above the first conveyor. The similar transfer apparatus orlift station is provided at the exit end of the upper conveyor formovement of a treated piece to a remote conveyor. The lift apparatus mayalso retrieve an untreated work piece from the remote conveyor andtransport it to the entrance end of the lower treatment conveyor.

[0012] In this way an untreated piece can be removed from the remoteconveyor, moved to the first or treatment conveyor, then moved to thesecond or drying conveyor and then retrieved from the drying conveyorand moved to the remote conveyor. As is seen the apparatus provides acircuit-like system for movement of the work pieces as well assubassemblies such as the travel mechanism, hoist mechanism and liftapparatus

BRIEF DESCRIPTION OF THE DRAWINGS

[0013]FIG. 1 is a side elevational view showing a circuit-like conveyingapparatus which includes a first or lower treatment line, a second orupper drying line, lift mechanisms at the end of the lines andmechanisms for raising, lowering and moving work pieces in the lowertreatment line.

[0014]FIG. 2 is an end elevational view taken along line 2-2 of FIG. 1showing the conveying apparatus frame, the upper and lower lines and atreatment tank positioned below the lower line.

[0015]FIG. 3 is a diagrammatic and perspective view showing work piecesassociated with a beam mechanism and positioned for lowering into aplurality of treatment tanks.

[0016]FIG. 4 is an end elevational view of a portion of the apparatus asseen in FIG. 2 showing a work piece positioned for lowering into atreatment tank.

[0017]FIG. 5 is a view similar to FIG. 3 showing the support beamlowered and work pieces lowered into a plurality of treatment tanks.

[0018]FIG. 6 is a view similar to FIG. 4 showing a work piece loweredinto a treatment tank.

[0019]FIG. 7 is a view similar to FIG. 5 showing the work pieces in thetanks and the rearward movement of the support beam.

[0020]FIG. 8 is a view similar to FIG. 6 showing a work piece supportedat the top of the tank and the support beam free to move rearwardly.

[0021]FIG. 9 is a perspective view of a fragment of the beam, hanger andtank showing the support beam moved downwardly and out of engagementwith the hanger mechanism.

[0022]FIG. 10 is a perspective similar to FIG. 7 showing the supportbeam raised and the work pieces raised from the tank and the beampositioned to receive a new work piece.

[0023]FIG. 11 is a perspective view similar to FIG. 10 showing thesupport beam and work piece being moved forwardly so as to index thesystem forwardly one unit.

[0024]FIG. 12 is a perspective and diagrammatic view of a circuit-likeconveying apparatus as in FIG. 1 and showing the travel and hoistmechanism for moving the support beam and lift mechanisms at the end ofthe conveyor lines.

[0025]FIG. 13 is a side elevational view of a portion of the lowerconveyor showing a hook mechanism for preventing the lowering of a workpiece.

[0026]FIG. 14 is a side elevational view showing a piston-and-cylinderapparatus for operating the hook mechanism.

[0027]FIG. 15 is a perspective view showing the hook mechanism.

[0028]FIG. 16 is side elevational view showing the hook mechanismgrasping a work piece.

[0029]FIG. 17 is a side elevational view showing the hook mechanism inan operative position to restrain a first work piece and a second workpiece in a lowered position.

[0030]FIG. 18 is an exploded perspective view showing the support beamand the travel and hoist mechanisms for causing the beam to index onestation and for raising and lowering the beam relative to the frame.

[0031]FIG. 19 is a diagrammatic and perspective view showing a pulleyand cable system for operating the hoist mechanism and a chain systemfor raising and lowering the beam.

[0032]FIG. 20 is similar to FIG. 19 but with the hoist mechanism andbeam in an extended position.

[0033]FIG. 21 is a plan view showing the travel and hoist mechanisms.

[0034]FIG. 22 is an elevational view showing the travel and hoistmechanisms connected to the beam and taken along line 22-22 of FIG. 21.

[0035]FIG. 23 is a side elevational view of a traveler mechanism andtaken generally along lines 23-23 of FIG. 21.

[0036]FIG. 24 is a perspective view of a lift mechanism whereby workpieces can be retrieved from one conveyor and moved to a secondconveyor.

[0037]FIG. 25 shows an arm and a saddle mechanism carried by the liftmechanism for engaging, supporting and moving a work piece and is takenalong line 25-25 of FIG. 24.

[0038]FIG. 26 is an end elevational view taken along line 26-26 of FIG.24 showing an arm or rail associated with the lift mechanism.

[0039]FIG. 27 is a side elevational view of the lift mechanism showingan arm with a work piece in various positions.

[0040]FIG. 28 is a plan-style view taken along line 28-28 of FIG. 27.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT I. The System Generally

[0041] Referring now to FIG. 1, there is shown a circuit-like conveyingsystem 10 generally which includes a lower or treatment conveying line12 generally, a lift or transfer mechanism 14 positioned at the end ofthe lower treatment line to retrieve work pieces therefrom. An upper ordrying conveying line 16 is provided to receive treated work pieces fromthe lift or transfer mechanism 14. A second lift mechanism 18 ispositioned at the end of the drying line 16 to retrieve dried workpieces therefrom and transfer those work pieces to a remote conveyor 20(see FIG. 12). Untreated work pieces can be moved from the remoteconveyor 20 to the entrance for the lower conveyor line 12. The workpieces are supported on a walking beam assembly 22 which is suspendedfrom a hoist mechanism 24 which cooperates with a travel mechanism 26that can be indexed forwardly one treatment station or backwardly onetreatment station.

[0042] The walking beam assembly 22, the hoist mechanism 24 and thetravel mechanism 26 are interconnected, interrelated and work togetherto transport, raise and lower work pieces. However, in the descriptionherein the assembly 22 and mechanisms 24 and 26 may be described orreferred individually.

[0043] The conveying system 10 includes a stationary support frame 28which supports the lower conveying line 12, the upper conveying line 16,the hoist mechanism 24 and the travel mechanism 26. As seen in FIG. 2, awork piece such as 30 is positioned above the treatment tank 32 forlowering into the tank 32 and subsequent treatment. It will also beappreciated that the circuit-like conveying system 10 has depth or isthree dimensional and accommodates wide work pieces such as 30. It isalso seen that the frame 28 spans a treatment tank such as 32.

[0044] The operation of the walking beam assembly 22 with respect to thework pieces and the hoist and travel operation is best seen in FIGS.3-11 inclusive. Referring to FIGS. 3, 5, 7, 10 and 11, the beam assembly22 includes a pair of spaced rails 22A and 22B. Associated with eachrail are L-shaped hanger engaging members such as 34. The beam assembly22 is raised and lowered by a plurality of chains such as 36. A workpiece hanger such as 38 is arranged to support a depending work piece 40and to engage the hanger engaging member such as 34. As seen in FIG. 3work pieces such as 40, 42 and 44 can be suspended from the beamassembly 22 over tanks such as 46, 48 and 50. Referring to FIG. 5, thebeam assembly 22 is lowered and the work pieces 40, 42 and 44 areimmersed in tanks 46, 48 and 50. The hangers such as 38 engage and reston the side of the tanks and the hanger engaging members such as 34 aredisengaged from the work pieces and can be moved to a position justbelow the hanger itself.

[0045] Then the beam 22 is no longer engaged with the hangers and can bemoved rearwardly one station as suggested in FIG. 7. Then referring toFIG. 10, the beam 22 is raised and as it is raised it engages thehangers for work pieces 40, 42 and 44. But it will be noted that therearward hanger engaging member is open (see FIG. 7) and can pick up anew work piece such as 52 in FIG. 10. Then the beam assembly 22 can bemoved forwardly as in FIG. 11 thereby indexing the work pieces onestation forwardly. It will be noted that each station is spaced the samedistance from an adjacent station.

[0046] Referring now to FIG. 4, the hanger 38 supporting the work piece40 and hanger engaging member bracket 34 are seen. In FIG. 6 the hanger38 is lowered to rest on the edge of the tank such as 46 and the hangerengaging member 34 is shown in engagement with the hanger and the workpiece 40 is shown there below. As seen in FIG. 8, the hanger engagingmember 34 is positioned below and disengaged from the hanger 38 and isin position to be moved rearwardly with respect to the tank.

[0047] Referring to FIG. 9, the hanger 38 is shown as a square tube andthe hanger engaging member 34 includes an angle iron 34A which ispositioned to engage the hanger 38 and support the same. It is seen thatbased upon the movement of the beam 22 downwardly, rearwardly, upwardlyand forwardly the work pieces are moved in a rectangular pattern so asto move the work piece from one tank to another.

[0048]FIG. 12 shows the entire circuit-like conveying apparatus 10 in adiagrammatic fashion. There the remote conveyor 20 and the liftmechanism 18 are shown whereby an untreated work piece can be removedfrom the conveyor 20, delivered to the lower conveyor line 12 onto thebeam assembly 22 so as to be moved to the treatment tanks, then moved tothe end of the conveyor 12 where the transfer mechanism 14 can retrievethe work piece and move it upwardly to the drying or upper conveyor 16.The upper conveyor 16 is a chain-like conveyor line that is positionedwithin an oven so as to form a drying line. Due to the heat to which thechain is exposed, the chain may lengthen and a take-up or tighteningmechanism is provided within the oven so as to adjust the chain.

[0049] Sometimes, it is desirable to prevent a work piece from beingimmersed or dipped in a particular tank. A hook assembly 50 is providedthat is secured to a stationary structure 51 secured to the frame 28(See FIGS. 1 and 13-17). The hook assembly includes an inverted U-shapedframe 52 that is secured to the stationary structure 51, two hingedlyconnected depending hooks 54 and 56 and an actuator bar 58 with anoutwardly extending arm 59 that connects the hooks 54 and 56 for jointmovement. A pneumatic cylinder 60 is connected at one end to the framesection 52 and at the other end to the actuator bar 58 via the arm 59.By retracting the piston the bar is rotated and the hooks 54 and 56raised to a nonengaging position. By extending the piston rod the hooksare rotated to a position so that when the other work pieces are loweredthe hooks engage a hangar such as 62 and prevent or restrain theassociated work pieces from being lowered. When the beam is raised formovement, the hooks can be rotated to an inoperative position and thepreviously restrained work piece engages the appropriate support on thebeam, the work piece is moved to the next position and can be loweredand raised the other work pieces as seen in FIG. 17.

II. The Travel and Hoist Mechanisms and Beam Assembly

[0050] The interrelations and interconnections of the travel and hoistmechanisms 24 and 26 and the beam assembly 22 are seen in FIGS. 18-23inclusive. For purposes of description these mechanisms and assemblieshave been described separately.

[0051] Referring first to FIG. 18 the stationary frame 28 includes anend section such as 70 and a pair of rails 72A and 72B. The travelmechanism 26 and hoist mechanism 24 are associated with the frame 28.The beam assembly 22 which supports the various hangers from the hoistmechanism by a plurality of spaced chains such as 74 and 76 and thepreviously identified chain 36. The chains are spaced along the lengthof the beam so as to evenly raise and lower the beam The chains arevertically orientated but trained about a plurality of verticallyorientated sprockets such as 78 and 80 which are secured to the travelframe 82 and rotate about a horizontal axis. The chains such as 74 and76 are trained about the sprockets and are secured at their end to thepull rods 84 and 86. The pull rods 84 and 86 are operated by a winch orspool 88 about which cables such as 90 and 92 are trained. A cable suchas 90 passes through a set of pullies which permit it to retract thepull rods such as 86. Those pullies include the horizontally arrangedpulley 94, the pulley 96 and the pulley 98. It will be noted that theend of the cable 90 is grounded or secured to the frame 82 at a point100 similarly the pullies 94 and 96 are secured to brackets that arealso grounded. As seen in FIGS. 19 and 20 by winding the cables 90 and92 about the drum 88 the pull rods 84 and 86 are retracted and thus drawthe frame assembly 22 upwardly through the action of the chains 74 and76 and other chains which are connected to the pull rod and the assemblysuch as 102 and 104. The frame 22 is shown in a lower position in FIG.20 in which the drum 88 is reversed and the weight of the frame 22 tendsto pull the frame downwardly and coacts with the pull rods 84 and 86 andchains 74, 76, 102 and 104. The spool 88, cables 90, 92, rollers 94, 96,98 and grounding position 100 can also be seen in FIG. 21.

[0052] Referring to FIG. 22 the hoist mechanism 24, the travel mechanism26 and the beam assembly 22 is seen in elevational view and the beamassembly 22 is in the upper position. As indicated above the entire beamassembly 22 and take up apparatus can be indexed one station forwardlyor one station rearwardly so as to remove the work pieces from a firsttank, raise them and move them to a second tank and then lower them.Referring to FIG. 18, horizontal movement of the beam assembly 22 iscontrolled by the travel motor 110 drive shafts such as 112 stops 114and 116 and the traveler or drive mechanism 118 generally (which is alsoseen in FIG. 23). Fundamentally the traveler 118 moves back and forthbetween the stops 114 and 116 along the chain 120. It is seen that withthe respect to the traveler movement the chain 120 is trained about anidler sprocket 122, a driven sprocket 124 and another idler sprocket126. Thus the motor 110 rotates the drive shaft 112 which causes thesprocket 124 to rotate. The chain 120 is drawn beneath the idlersprocket 122 over the drive sprocket 124 and beneath the idler sprocket126 to cause the traveler mechanism 118 to move toward one of the stops114 or 116. It will be appreciated that when the traveler mechanismmoves the hoist mechanisms 24 similarly moves and so does the walkingbeam assembly 22. The mechanism is then reversed and the walking beam ismoved to the other end at stop 114. At that point the beam 22 may beraised so as to lift the appropriate hangers and thus the work pieceshave been indexed or moved one station forwardly.

III. The Transfer or Lift Mechanism

[0053] The transfer or lift mechanism can be seen in FIGS. 24-28inclusive. However, reference is made to FIG. 12 where the liftmechanisms 14 and 18 are shown at either end of the conveyor wherebywork pieces can be lifted by a lift mechanism 14 from the end of thelower line 12 to the line 16. Other lift mechanism can move dried workpieces from the upper line 16 to the remote conveyor 20 and from theremote conveyor 20 untreated pieces can be removed and delivered to thelower conveyor 12.

[0054] Referring now to FIG. 24, a lift mechanism 150 generally isshown. The lift includes a pair of side posts 152 and 154 which togetherwith cross members 156 and 158 define a frame. Within the frame there isprovided a carrier 160 generally which can be moved vertically upwardlyor downwardly in the larger frame. A pair of arm assemblies 162 and 164are secured to the carrier and can move inwardly or outwardly and fromone side to the other side of the carrier 160. The carrier 160 includesan upper cross member 166 and a lower cross member 168. A pair ofvertical members 170 and 172 connect the cross members 166 and 168 andcooperate the posts 152 and 154 which have rails therein.

[0055] The carrier 160 is raised or lowered by a driven chain andcounter weight mechanism. The drive motor 174 is connected via a shaftsuch as 176 to chain drive sprockets 178 and 180 on the opposite sidesof the lift. At the top of the lift mechanism idler sprockets 182 and184 are provided. Drive chains 186 and 188 are trained about the drivesprockets such as 178 and 180. The chain such as 186 is connected to thecarrier 160 by a bar such as 189. The chain 186 is also connected to thecounter weight 190 but on the opposite side of the chain. Thus the motor174 can drive the chain so that the counter weight 190 moves upwardlyand the carrier 160 via bar 189 descends. If the motor 174 is reversedthe counter weight 190 is moved downwardly and the carrier 160 is movedupwardly. Each of the arms 162 and 164 are secured to one of therail-like members 170 and 172 at a position spaced from the top crossmember 166 by brackets 171 and 173. Each of the arms includes astationary section such as 192 and a telescoping section such as 194.The telescoping section rides on a I-beam like rail 196 as seen in FIG.26. On each telescoping section such as 194 a hanger supporting saddlesuch as 198 or 199 is mounted. The carrier motor 200 and carrier driveshafts 202 and 204 cause the carrier chains 210 and 212 to rotate tocause the telescoping sections of the arms to move inwardly or outwardlyas seen in FIG. 24. It will be noted that the carrier cross member 166is spaced above the connection of the arm to the carrier so as to permitthe saddle 198 to move thereunder. Moreover, the entire carrier is sizedso as to permit clearance of a work piece suspended from saddles such as198 and 199. The carrier chain 212 is connected to the telescopingsection 194 by a pinion 213 and rack 214 which cooperate to cause thearm to move laterally inwardly and outwardly.

[0056] The saddle 198 is connected to one end of the telescoping sectioncable 216. The cable 216 is trained about the idler 218 and secured tothe telescoping section at an end 220. The saddle 198 is also connectedto a second telescoping section cable 222 which is trained about a idler224 and connected to the telescoping section at end 226. Thus as the armmoves from one side of the carrier to the other side of the carrier itwill be seen that the saddle will move relative to the telescopingsection 194 and from one side of the carrier to the other side of thecarrier 160. This is seen in FIG. 27 where the stationary arm 192 andthe telescoping arm 194 are shown. In this situation a saddle such as198 is shown supporting a hanger such as 226 and work piece such as 228.It will be appreciated that the telescoping section 194 of the arm aswell as the hanger 226 and work piece 228 is moved from one side of thepost 152 and carrier 160 to the other side (i.e. left to right or viseversa). It is seen that in FIG. 27 the arm can be moved to a lowerposition or raised to an upper position and the saddle 198, hanger 226and work piece 228 can move accordingly.

IV. Operation

[0057] In operation an untreated work piece is delivered on a remoteconveyor 20 so that a lift mechanism such as 18 can position atelescoping section such as 194 and hanger receiving saddles such as 198and 199 under the hanger for the work piece and thus remove the workpiece from the remote conveyor. The hanger rests on the saddles and thesection is retracted under the action of the drive motor 200. Thetelescoping sections of the arms are moved to the other side of the liftand in position to be delivered to the treatment conveyor line such as12. There the hanger and work piece are deposited on the hanger engagingbracket such as 34 associated with the beam 22 and the untreated piecesare added to the conveyor and moved as shown in FIGS. 3, 5, 7, 10 and11. The hoist and travel mechanisms 24 and 26 cause the untreated pieceto move into and out of the various treatment tanks and to the exit endof the lower line. At the exit end of the lower line 26 a lift mechanism14 is provided and arms on the lift mechanism are extended and engagethe hanger on the appropriate saddles. The arm is then retracted andlifted to the second line such as 16. There the arms extend and thehanger is deposited on the line 16. The treated piece is moved along thesecond or drying line to its exit end. There the lift mechanism 18extends the arms and engages the hanger using the saddles. The arms areretracted, moved to a lower position, and caused to move to the otherside of the lift mechanism and the hanger and work piece are depositedon the remote conveyor 20. The cycle is then repeated. It will beappreciated the appropriate controls are provided for the operation ofthe system.

[0058] Numerous changes can be made to the embodiment disclosed hereinwithout departing from the spirit and scope of this invention.

What is claimed is:
 1. A conveyor apparatus for the simultaneous anddiscontinuous movement of a plurality of work pieces to and between aplurality of treatment stations, said apparatus including: an elongatedand stationary structural frame having an entrance end and an exit end;a plurality of treatment stations positioned along the length of theframe and in spaced relation thereto; a travel mechanism carried on theframe and moveable relative to the frame between adjacent treatmentstations; a hoist mechanism carried on the travel mechanism and havingretractable and extendable members; and an elongated beam which extendsalong the frame, which is connected to the hoist mechanism by theretractable and extendable members and which is constructed for movementbetween a lower position and an upper position and to releasably supporteach of a plurality of work pieces; so that the beam can be lowered forthe work pieces to be treated, moved one station towards the entranceend, raised and moved one station toward the exit end so as to move thework pieces forwardly one station.
 2. An apparatus as in claim 1 whereina hook assembly is mounted to the structural frame for engaging a workpiece and to prevent the work piece from being lowered with other workpieces on the beam, said hook assembly including a bracket mounted tothe frame, a pair of hook members hingedly mounted to the bracket and anactuator for moving the hook members between a grasping position and anon-grasping position.
 3. An apparatus as in claim 1 wherein saidstructural frame includes spaced stop members for limiting movement ofthe travel mechanism, and said travel mechanism includes a driveassembly for causing the travel mechanism to move between the stopmembers.
 4. An apparatus as in claim 3 wherein the drive assemblyincludes a traveler mechanism which includes a chain which extendsbetween stop members, a drive sprocket for engaging the chain, a drivemotor for rotating the drive sprocket and causing the travel mechanismto move along the chain between stop members.
 5. An apparatus as inclaim 1 wherein the retractable and extendable members include a pair ofelongated pull rods each ending along the frame, spaced andsubstantially parallel to each other, a spool member secured to thetravel mechanism, and a pulley and cable system connected to the spoolmember and to each of the pull rods so that winding of the cable aboutthe spool causes the pull rods to move in one direction and unwindingpermits the pull rods to move in the opposite direction.
 6. An apparatusas in claim 5 wherein a plurality of sprockets are mounted to the travelmechanism, and a plurality of support chains are provided, eachconnected at one end to the elongated beam and at the other end to apull rod and each trained about a sprocket so that the beam is raised orlowered by movement of the pulls rods.
 7. An apparatus as in claim 1wherein each beam includes work piece hangers or grasping elements forsupporting a work piece and for releasing a work piece for treatment. 8.A transfer or lift apparatus for retrieving a work piece on a hangerfrom a first position and transporting the work piece to a secondposition, said apparatus including: a substantially vertical frame-likestructure; a carrier assembly mounted in the frame-like structure formovement upwardly and downwardly in the frame-like structure andincluding a pair of generally horizontally positioned arm assembliesmounted to the carrier, each of said arm assemblies including ahorizontally extendable and retractable section for movement toward andaway from the carrier assembly; and a work piece grasping structuremounted to the extendable and retractable section of said arm formovement with the arm to a position toward the end thereof when the armextended from the carrier.
 9. An apparatus as in claim 8 wherein thereis provided a drive assembly associated with the frame-like structureand carrier assembly for moving the carrier assembly upwardly ordownwardly in the frame-like structure.
 10. An apparatus as in claim 9wherein the drive assembly includes a drive motor, a drive sprocketconnected to the drive motor for rotation by the drive motor, and adrive chain arranged for engagement by the sprocket and connected to thecarrier assembly for movement of the carrier assembly.
 11. An apparatusas in claim 9 wherein there is provided a counterweight connected to thedrive chain for cooperation in moving the carrier assembly.
 12. Anapparatus as in claim 10 wherein each of said arm assemblies include astationary portion mounted to the carrier and said horizontallyextendable or retractable section telescopically engages said stationarysection for movement relative to the stationary section, and a hangergrasping saddle member moveably mounted on the telescoping section. 13.An apparatus as in claim 14 wherein the hanger grasping section isconstructed to move said telescoping section in relation to movement ofthe telescoping section.
 14. An apparatus as in claim 15 wherein thetelescoping section includes a rack-like gear and a rotatable drivesprocket is provided and engages the rack-like gear so as to move thetelescoping section upon rotation of sprocket.
 15. A circuit-likeconveyor system which includes: a lower conveyor line having an entranceand an exit end; a first lift mechanism positioned adjacent the exit endof the lower line; an upper conveyor line spaced from the lower line andhaving an entrance end and an exit end, with the first lift mechanismpositioned adjacent the entrance end of the upper conveyor line; asecond lift mechanism positioned adjacent the exit end of the upper lineand the entrance end of the lower line; and constructed for thesimultaneous and discontinuous movement of a plurality of work pieces toand between a plurality of treatment stations; an elongated andstationary frame; said plurality of treatment stations positioned inspaced relation to the frame; and said lower conveyor line; a travelmechanism carried on the frame and movable relative to the frame betweenadjacent treatment stations; a hoist mechanism carried on the travelmechanism and having retractable and extendable supports; an elongatedbeam which extends along the frame and which is connected to the hoistmechanism by the retractable and extendable supports and which isconstructed for movement between a lower position and an upper positionand to releasably engage each of a plurality of work pieces; and whichis constructed for movement toward the entrance end or toward the exitend of the lower conveyor so that the beam can be lowered and workpieces delivered to the treatment stations; moved one station toward theentrance end of the lower conveyor, raised, and moved one station towardthe exit end so as to move the work pieces forwardly one station; andwherein each of the lift mechanisms is constructed to retrieve a workpiece on a hanger from a first position and transport the work piece toa second vertically different position, and each mechanism includes: asubstantially vertical frame-like structure; a carrier assembly mountedin the frame-like structure for movement upwardly and downwardly andincludes a pair of generally horizontally positioned arm assembliesmounted to the carrier, each of said arms including a section which ishorizontally extendable and retractable for movement toward and awayfrom the carrier assembly; and a work piece receiving structure mountedto the extendable and retractable portion of each arm for movement withthe arm to a position toward the end thereof when the arm is extendedfrom the carrier.